A) Field of the Invention
The present invention relates to a semiconductor device and its manufacture method, and more particularly to a semiconductor device using dielectric having a low dielectric constant (low-k) as an interlayer insulating film.
B) Description of the Related Art
High integration and high speed operation of semiconductor integrated circuit devices lead to finer transistors and finer wirings. An operation speed of a semiconductor device is greatly influenced by a time constant RC (R: resistance, C: parasitic capacitance) of wirings. As wirings are made finer, a wiring pitch becomes narrow and a wiring width is narrowed. As a cross sectional area of a wiring reduces, a resistance R increases.
In order to lower the resistance of a finer wiring, a copper wiring has been used in place of an aluminum wiring. Since a precision of etching a copper wiring is low, a damascene (buried) wiring has been adopted. Wiring trenches and via holes are formed in an insulating film, a copper wiring constituting wiring patterns and via conductors is buried in the trenches and via holes, and unnecessary copper wirings are removed by etch-back or chemical mechanical polishing (CMP).
A wiring height is made high to prevent an increase in resistance while a wiring width is maintained narrow. If insulating films for electrically insulating wirings are made of the same material and if the wiring pitch is narrowed and the wiring height is increased, a parasitic capacitance of wirings increases. An increase in the parasitic capacitance prevents a high speed operation of the semiconductor device. It has been desired to change the material for insulating wirings, from silicon oxide having a relative dielectric constant of about 4.2 to a material having a lower dielectric constant.
One of insulating materials having a low-k is porous silicon oxide (silica) formed from a silicon oxide base material changed to a porous state. Assuming that pores are filled with vacuum or gas, the relative dielectric constant of pores is about 1 and it is expected that the dielectric constant becomes lower as a pore ratio is raised.
As the pore ratio of porous silicon oxide is raised, although the dielectric constant lowers correspondingly, a mechanical strength of the film represented by Young's modulus and hardness lowers. If multi-layer wirings are formed by using interlayer insulating films made of a porous silicon oxide film having a low mechanical strength, interlayer cracks are likely to be formed by thermal and mechanical stresses during forming multi-layer wirings and stresses during package sealing.
Adhesion properties are poor between a porous or non-porous low-k insulating film and an insulating film such as a silicon nitride film to be used for an etching mask or a CMP stopper. In order to improve adhesion properties, it has been proposed to change properties of an underlying film surface before an insulating film is formed. Changing processes disclosed to date include a method of roughing an underlying surface by exposing to argon plasma to increase an anchoring force, or lowering an F concentration of an SiOF film surface, a method of roughing a film surface by applying ultrasonic vibrations, a method of oxidizing a film surface by irradiating ultraviolet rays, and other methods.